Guyz!! Which kind of ad units have performed best for you? For me it has always been Text ads with rectangle and link unit.
both, it is very rare i restrict it to one format. sometimes i could because for one ad unit images work better than text, but the problem is you can only restrict to text only or everything else only. You can't restrict to images only, so you get flash, video, rich media crap which in those cases don't perform well, so ad impressions will be wasted on those, and it's still better to have text ads getting some of the ad impressions. So it is very rare i restrict some ad units, sometimes i put text only to avoid those other formats, despite static images not performing that bad.
It is better one text link with 336x280 zise, keep maintaining your traffic, and more traffic is better to get click for the ads.